1.Field
The present disclosure relates to an organic light emitting diode display device.
2. Related Art
Recently, the development of various flat panel displays (FPDs) has been accelerated. Among them, an organic light emitting diode display device uses an emissive device, thereby obtaining an advantage that a response speed is fast, and light emitting efficiency, luminance and a viewing angle are large.
In the organic light emitting diode display device, each pixel has an organic light emitting diode. The organic light emitting diode includes an organic compound layer formed between an anode electrode and a cathode electrode. The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). If a driving voltage is applied to the anode electrode and the cathode electrode, holes having passed through the hole transport layer (HTL) and electrons having passed through the electron transport layer (ETL) are moved to the emission layer (EML) to form excitons, so that the emission layer (EML) generates a visible light.
In the organic light emitting diode display device, pixels including the organic light emitting diodes are arranged in a matrix form and the brightness of the pixels is controlled according to the grayscale of video data. The organic light emitting diode display device selectively turns on TFTs (active elements) to select pixels, and maintains the emission of pixels by voltages stored in storage capacitors.
Such an organic light emitting diode display device compensates for a variation in a threshold voltage of a driving TFT through a voltage compensation driving method. In the organic light emitting diode display device for voltage compensation, a storage capacitor is connected to the gate of the driving TFT, and a sampling TFT is connected between the gate and drain of the driving TFT and is turned on to allow the driving TFT to be in a diode connection state, so that the threshold voltage of the driving TFT is stored in the storage capacitor.
In the organic light emitting diode display device using the voltage compensation driving method, a threshold voltage compensation error rate significantly varies depending on parasitic capacitances existing in the driving TFT and the sampling TFT. Therefore, even when pixels are appropriately designed, the threshold voltage compensation error rate reaches about 10% to 15%. Due to such a threshold voltage compensation error, luminance unevenness or an afterimage problem is serious.